Mediated communication between public spaces is a relatively new concept. One current example of this interaction is video conferencing among people within the same organization. Large scale video-conferencing walls have begun to appear in public or semi-public areas such as workplace lobbies and kitchens. These connections provide a link via audio and/or video to another public space within the organization. When placed in public or semi-public work spaces, they are often designed for casual encounters among people within that community. Thus far, communicating via these systems has not met expectations. Some drawbacks to such systems have been lack of privacy, gaze ambiguity, spatial incongruity, and fear of appearing too social in a work environment. In this talk, I discuss a different goal and approach to linking public spaces. We are not creating a substitute for face-to-face interaction, but rather new modes of conversational and physical interaction within this public space. This is accomplished through the introduction of what we are defining as a social catalyst. We address the need for designs best suited for linking public spaces and present a series of design criteria for incorporating mediated communication between public and semi-public spaces.